The present invention relates a method for the oxidation of silicon and the formation of silicon oxide regions by implantation of fluorine into the silicon lattice and subsequently forming an oxide region by a typical oxide growth process.
In the fabrication of a MOS (metal oxide semiconductor) semiconductor device, it is essential to form a gate oxide film by oxidation. The properties of a gate oxide film are greatly influenced by the atmosphere under which the film is formed. Accordingly, an oxide film can be deposited by processes differing from each other in atmospheric conditions. For instance, a silicon oxide film can be deposited by any of the processes belonging to, for example, the families of dry oxidation and wet oxidation. The dry oxidation process comprises supplying a sufficiently dried high purity oxygen to the surface of a hot silicon substrate. In this manner, a silicon oxide film can be formed on the surface of the silicon substrate. The wet oxidation process comprises supplying, to the surface of a silicon substrate, a hot carrier gas containing water vapor. This process also provides a silicon oxide film on the surface of the silicon substrate.
The presence of either chlorine or fluorine in an ambient of dry oxygen is known to accelerate the oxidation rate. It is known that a dry oxidation method to form a silicon oxide film under an oxidizing atmosphere based on a compound containing chlorine (e.g., HCl, Cl2, CCl4, C2HCl3, CH2Cl2, and C2H3Cl3) or a compound containing a halogen atom other than chlorine provides a silicon oxide film which yields an oxide film thicker than that produced by the dry oxidation method alone. In this regard, fluorine is much more efficient than chlorine. Typically, chlorine is added as a percentage of the total oxygen flow, whereas fluorine on the order of parts-per-million will have a noticeable effect on the oxidation rate.
However, these prior art processes often require additional processing steps, such as annealing, to form a sufficient oxide layer. Additionally, the prior art methods do not allow the growth of the field oxide regions and the gate oxide regions during a single oxide growth step. The present invention overcomes the drawbacks of the prior art methods.
The present invention relates to method for the oxidation of a semiconductor substrate and the formation of oxide regions or layers by implantation of fluorine into the silicon lattice and subsequently forming an oxide region by a typical oxide growth process. The oxide growth process may be a thermal oxidation process such as dry or wet ambient oxidation processes.
The oxide growth depends upon the amount of fluorine implanted into the substrate, the depth which the fluorine is implanted and the energy at which the fluorine is implanted. The process according to the present invention allows for the simultaneous growth of oxides having different thicknesses at the same time by tailoring the fluorine implantation. Additional advantages of the present invention will be apparent from the detailed description and drawings, which illustrate preferred embodiments of the invention.